Musculoskeletal disorders
among workers in plastic
manufacturing plants
Distúrbios músculo-esqueléticos
em trabalhadores da indústria de
plásticos
Rita de Cássia Pereira Fernandes
IAda Ávila Assunção
IIAnnibal Muniz Silvany Neto
IFernando Martins Carvalho
II Departamento de Medicina Preventiva e Social da Faculdade de Medicina da
Universidade Federal da Bahia
II Departamento de Medicina Preventiva e Social da Faculdade de Medicina da
Universidade Federal de Minas Gerais
Correspondência: Rita de Cássia Pereira Fernandes. Departamento de Medicina Preventiva e
So-cial. Faculdade de Medicina da Universidade Federal da Bahia. Rua Machado Neto, 223 apto. 1403 – Pituba - Salvador, BA - CEP: 41.830-410. E-mail: ritafernandes@ufba.br
Abstract
Background: Epidemiological studies have indicated an association between musculo-skeletal disorders (MSDs) and physical work demands. Psychosocial work demands have also been identified as possible risk factors, but findings have been inconsistent. Object-ives: To evaluate factors associated with up-per back, neck and upup-per limb MSD among workers from 14 plastic manufacturing companies located in the city of Salvador, Brazil. Methods: A cross-sectional study design was used to survey a stratified pro-portional random sample of 577 workers. Data were collected by questionnaire inter-views. Factor analysis was carried out on 11 physical demands variables. Psychosocial work demands were measured by demand, control and social support questions. The role of socio-demographic factors, lifestyle and household tasks was also examined. Multiple logistic regression was used to identify factors related to upper back, neck and upper limb MSDs. Results: Results from multiple logistic regression showed that distal upper limb MSDs were related to manual handling, work repetitiveness, psychosocial demands, job dissatisfaction, and gender. Neck, shoulder or upper back MSDs were related to manual handling, work repetitiveness, psychosocial demands, job dissatisfaction, and physical unfitness. Conclusions: Reducing the prevalence of musculoskeletal disorders requires: improv-ing the work environment, reducimprov-ing biome-chanical risk factors, and replanning work organization. Programs must also be aware of gender specificities related to MSDs. Keywords: Ergonomics. Musculoskeletal disorders. Repetitive strain injury. Upper limb disorders. Psychosocial.
Resumo
Introdução: Estudos epidemiológicos têm indicado uma associação entre distúrbios músculo-esqueléticos (DME) e demandas físicas no trabalho. Demandas psicossociais no trabalho também têm sido identificadas como possíveis fatores de risco, mas os acha-dos são inconsistentes. Objetivos: Avaliar fatores associados aos DME em região alta do dorso, pescoço e extremidades superiores entre trabalhadores de 14 fábricas de plástico na Região Metropolitana de Salvador, Brasil. Métodos: Estudo de corte transversal foi realizado para avaliar uma amostra aleatória estratificada proporcional de 577 trabalha-dores, utilizando questionário administrado por entrevistador. Análises fatoriais foram realizadas com as 11 variáveis relacionadas a demandas físicas, resultando em dois fatores. Demandas psicossociais no trabalho foram medidas através de questões para demanda psicológica, controle e suporte social. A importância das variáveis sociodemográfi-cas, de estilo de vida e trabalho doméstico também foi examinada. Regressão logística múltipla (RL) foi utilizada para identificar fatores relacionados com DME em região alta do dorso, pescoço e extremidades superiores. Resultados: Resultados da RL mostraram que DME em extremidades superiores distais estão relacionadas com manuseio de carga, repetitividade, demandas psicossociais, insa-tisfação no trabalho e ser do sexo feminino. DME na região alta do dorso e pescoço estão associados ao manuseio de carga, repetitivi-dade, demandas psicossociais, insatisfação no trabalho e condicionamento físico pre-cário. Conclusões: Reduzir a prevalência de DME requer medidas que reduzam as demandas físicas no trabalho e ao mesmo tempo promovam mudanças na organização do trabalho, visando a reduzir as demandas psicossociais. Os programas devem ser sen-síveis a uma provável diferença de gênero na ocorrência de DME.
Palavras-chave: Ergonomia. Distúrbios músculo-esqueléticos. LER. DORT. Distúr-bios ocupacionais de membros superiores. Fatores psicossociais no trabalho.
Introduction
Musculoskeletal disorders (MSDs) are an important public health problem in both developed and developing countries, with substantial impact on quality of life and a substantial economic burden in compen-sation costs, lost wages and productivity1-3.
In Brazil, the most common occupatio-nal health problem is MSDs, according to data from The National Institute of Social Security4. Descriptive studies on MSDs
among industrial populations have focused on workers that experience chronic pain and are on long-term paid sick leave due to temporary or permanent disability. Incre-asing the knowledge about active workers who exhibit MSDs symptoms provides the opportunity to assess potential risk factors and to implement control measures. This could prevent the development of incapa-citating clinical conditions.
Epidemiological studies indicate an association between MSDs and physical
demands at work5-10. Psychosocial demands
have also been identified as possible risk factors for MSDs11-16.
Non-occupational factors such as obesity, sports activities and gender have also been associated with MSDs, but the findings of previous studies have been in-consistent17-20.
The aim of this study was to identify the factors associated with MSDs among workers who were employed in plastic ma-nufacturing plants.
Methods
A cross-sectional study was conducted on a target population of all workers perfor-ming maintenance and operation activities in 14 plastic plants in the city of Salvador, Brazil. The plants were representative of factories in the Salvador Metropolitan Area. The decision to select companies from the plastics industry was based on the presen-ce of epidemiological, technological and social considerations. Work processes in the plastics industry are associated with
repetitiveness, use of force, and a highly demanding work pace. Details on the type of work performed in those plants, types of work shifts and gender characteristics of the worker population were published elsewhere21,22.
There were 1,177 eligible workers in 14 factories, the number of workers varying from factory to factory. A proportional and stratified random sample, comprising 577 subjects, was selected. In this sample, the number of workers was such that the proportional participation of workers from each plant did not change. The sample was calculated considering a degree of precision of 4.0%, a level of significance of 95.0%, an expected MSDs prevalence of 50.0%, and a design effect of 1.4.
Data were collected in the year 2002, by a pre-tested questionnaire administered by trained interviewers. The interviews took place within each participating company, during a work day, in a place set aside for this purpose.
Collected data included sociodemo-graphic information, occupational history (including periods of formal and informal employment), daily and weekly working hours, physical demands of work, physical environment of the workplace, psychosocial demands of the work (Karasek, 198523,24),
tobacco use, medication use, alcohol con-sumption, housework, physical fitness, MSDs, and other health information (e.g. previous bone fractures, history of diabetes, rheumatoid arthritis or hypothyroidism). Physical fitness was assessed based on the workers’ answers regarding the perception of their own (physical) fitness. The response scale had six ordinal descriptors (0 to 5), including two anchors at extreme levels (poor; excellent).
The questionnaire used in this study is a translation to Portuguese of the Nordic Musculoskeletal Questionnaire (NMQ)7,25,
with questions to evaluate the severity, duration and frequency of symptoms in all body areas. The Nordic Musculoskele-tal Questionnaire is the most widely used survey tool to measure the prevalence of
musculoskeletal disorders. Results showed a percentage of agreement higher than 80% in the test-retest method to evaluate reliability and in validity tests against clinical history
25,26. In Brazil, results of a study by Pinheiro et
al. (2002)27 revealed an 86% agreement rate
between symptoms reported in the NMQ and the respondent’s clinical history.
The case definition of MSDs in distal upper limbs included reporting pain or discomfort (symptoms of pain, numbness, tingling, burning and swelling) in fingers, wrists, hands, forearms or elbows, with or without pain in other body areas, over the past twelve months of work that lasted at least one week or occurred at least once a month, and had not been caused by an acute injury, and in which one of following conditions applied: current symptom se-verity rating was 3 or greater (0 - 5 scale) or sought medical attention or lost time (official or unofficial) or changed to light or restricted work (official or unofficial) or changed jobs because of these problems. All workers who presented pain or discomfort in the neck and/or shoulder and/or upper back, with or without pain in other body seg-ments, with the criteria mentioned above, were considered to be cases of MSDs of the neck, shoulder and upper back.
Physical demands of work were evalua-ted by means of workers’ answers, on a scale ranging from 0 to 5 (regarding duration, frequency or intensity of physical work). Questions about repetitive movements with hands, force exerted with arms or hands, seated, standing or walking posture while working, arms raised above shoulder height, trunk inclined forwards and rotated, lifting loads, and contact pressure were selected for analysis.
Psychosocial aspects of work were me-asured by means of the Job Content Ques-tionnaire (JCQ). The questions in the JCQ allowed scores for psychological demands, control or decision latitude and social support to be obtained. A psychosocial exposure variable was defined from these scores. Criteria for high exposure were high psychological demands, low control and
low support. Fulfillment of at least two of these criteria characterized high exposure to psychosocial demands. Low psychosocial exposure criteria were low psychological demands, high job control and high social support. At least two of these criteria for low psychosocial exposure had to be met in order to assign a subject in this group14.
Questions from the JCQ23 were also used to
evaluate job dissatisfaction.
As the variables measuring physical demands of work could be related to each other, a matrix of Spearman correlations was analyzed. Following, a decision was made to reduce the 11 variables, using factor analysis28.
Multivariate analysis was conducted by means of unconditional logistic regression (LR). Modeling started by preselecting inde-pendent variables based on the biological plausibility of associations and on univa-riate LR. Variables were selected using the backward stepwise method. The likelihood ratio test and 95% confidence intervals were used. In the LR diagnosis, the Hosmer-Lemeshow goodness-of-fit test and residual analysis were used29.
Several authors cited by Hosmer and
Lemeshow29 strongly recommended the
use of an alpha between 0.15 and 0.20 for removing variables in regression and dis-criminant analyses, and there are grounds for also applying it to LR analysis. However, the present authors chose to use a more conservative alpha, i.e. 0.05.
The study was approved by the Research Ethics Committee of the Institute of Public Health of the Federal University of Bahia.
Results
The study population comprised 577 workers, 31% were women. Sixty-three percent of workers worked shifts and 70% reported working overtime. The workers had a mean length of employment of 14.3 years in the formal or informal labor market. The mean number of hours worked per week was 43.9 hours (Table 1).
Table 2 shows the distribution of 11
physical work demand variables. Repeti-tive movements were frequent, especially among women. With regard to general body posture while working, almost all the work was performed while standing. The tasks of men were more dynamic and as conse-quence they had to adopt a walking posture more often. Men spent almost all their time at work walking, whereas women reported much less movement away from their work stations. Load-lifting activities were more frequently mentioned by men.
Women reported they had less control over their work, suffered greater psycho-logical demands and received less social support than men. They also showed greater job dissatisfaction (Table 3).
Prevalence of distal limb MSDs (elbow, arm, wrist, hands or fingers) was 35% among female workers and 12% among male workers. For neck, shoulders or upper back MSDs, the prevalence was 27% and 18% among female and male workers, respectively.
Factor analysis produced two principal components of the original set of 11 phy-sical exposure variables. In a decreasing order of the weights presented by each variable, these components were as follo-ws: variable 1 characterized the physical demands relating to load handling and related tasks, and included load lifting, standing posture while working, muscular exertion using arms or hands, working with arms raised above shoulder level, working with trunk rotated, physical hand pressure on the work object, and inclined trunk. Variable 2 characterized repetitive physical demands and included static postures of the trunk while working with the hands in a seated posture. These variables were used as the physical demand variables in the LR analysis. Furthermore, the demands/ control/support model variables, which are described separately in Table 3, constituted a single variable that measured psychoso-cial exposure in the LR, in accordance with criteria already described.
Tables 4 and 5 present the results from the multiple LR analysis. The
goodness-of-fit test and residual analyses showed that the final models were a good fit. The inde-pendent variables in the complete models were age, sex, schooling, and marital status; overtime, length of service in the company, number of years of work (including formal and informal jobs), job dissatisfaction, physical demands consisting of manual handling, physical demands consisting of repetition, psychosocial demands; use of alcoholic drinks, smoking, physical fitness, overweight/obesity, number of hours of housework per week.
Gender, psychosocial demands, and job dissatisfaction all showed significant associations with MSDs of the distal upper limbs (Table 4). There were two variables that presented borderline results (with intervals including the unit), Physical
De-mands with Repetitiveness, OR 1.62 (95% C.I. 0.97 – 2.70), and Physical Demands with Manual Handling, OR 1.56 (95% C.I. 0.95 – 2.58) (data not shown).
The OR of neck, shoulders and upper back MSDs was 2.96 when comparing workers who were exposed to physical work demands related to manual handling to those with less exposure to such demands. MSDs of the neck, shoulders and upper back were also significantly associated with repetitive physical demands, psychosocial demands, job dissatisfaction and poor phy-sical fitness (Table 5).
Discussion
Results revealed that women had greater exposure to repetitive hand movements and Table 1 - Sociodemographic and occupational variables, according to gender.
Tabela 1 – Variáveis sociodemográficas e ocupacionais, segundo sexo
Variables Study population
n=577 (%)
Female n=179 (%)
Male 398 (%)
Age (mean of years± sd) 31.5 ± 8.2 31.6 ± 8.4 31.4 ± 7.7
Marital status*
Married or living together Single or living alone
350 (61) 226 (39) 91 (51) 88 (49) 259 (65) 138 (35) Education Level ≥ 11 years <11 years 240 (42) 337 (58) 74 (41) 105 (59) 166 (42) 232 (58) Double working shift*
Yes No 66 (12) 510 (88) 17 (10) 161 (90) 49 (12) 349 (88) Working hours schedule*
Shift work Regular 362 (63) 214 (37) 101 (56) 78 (44) 261 (66) 136 (34) Exceeding hours of work *
Yes No 406 (71) 170 (29) 146 (82) 33 (18) 260 (66) 137 (35) Hours of housework per week *
≥20 < 20 101 (17) 476 (83) 78 (44) 101 (56) 23 (6) 375 (94)
Years of formal or informal jobs (mean ± sd)* 14.3 ± 8.8 12.4 ± 8.3 15.1 ± 8.9
Years of employment in current job (mean ± sd)* 3.8 ± 4.3 3.6 ± 3.9 3.9 ± 4.5
Hours of work (in last week) in current job (mean ± sd)* 43.9 ± 8.6 45.5 ± 7,7 43.1 ± 8.9
Hours of domestic work in the last week (mean ± sd)* 8.8 ± 10.0 17.1 ± 11.4 5.0 ± 6.8
*P < 0.05 (comparisons of means by analysis of variance and comparisons of proportions by chi square test) / comparações de médias por análise de variância
working in a general body static posture (more standing than seated). Men’s work was characterized by slightly more load lif-ting and a general body posture of dynamic work that implied walking more during the working day. These different patterns of
exposure reflect the different tasks assigned to men and women at the workplace.
The prevalence of MSDs was higher among women, particularly for distal upper limbs (35% versus 12%). Considering that this prevalence is related to symptoms Table 2 - Physical (postures and movements) work demands.
Tabela 2 – Demandas físicas (posturas e movimentos) no trabalho. Physical demands
(0 – 5 points)
Study population Female Male
(mean ± sd) Repetitive gesture**
0=never 5=very frequent
3.7 ±1.5 4.2±1.4 3.5±1.6
Force with the arms or hands 0=very weak 5=very strong
3.4 ±1.4 3.4±1.4 3.4±1.4
Sitting posture**
0=not at all 5=all the time
1.0±1.5 1.3±1.7 0.9±1.3
Standing posture** 0=not at all 5=all the time
4.2±1.3 4.0±1.5 4.3±1.1
Walking**
0=not at all 5=all the time
3.3±1.7 2.5±1.8 3.7±1.4
Arms above the height of the shoulders* 0=not at all 5=all the time
1.7±1.6 1.5±1.6 1.8±1.5
Repetitive movements with the hands** 0=not at all 5=all the time
4.1±1.3 4.5±1.0 3.9±1.4
Bent trunk**
0=not at all 5=all the time
2.7±1.7 3.0±1.8 2.5±1.6
Turned trunk**
0=not at all 5=all the time
2.5±1.8 2.8±1.9 2.3±1.8
Lifting weights** 0=not at all 5=all the time
2.4±1.7 1.8±1.8 2.6±1.6
Mechanical pressure with the hands on the object of work 0=very weak 5=very strong
3.0±1.4 3.1±1.5 3.0±1.4
*P < 0.05; **P < 0.001 (comparisons of means by analysis of variance) / (comparações de médias por análise de variância).
Table 3 - Psychosocial work demands.
Tabela 3 – Demandas psicossociais no trabalho.
Psychosocial demands Study population Female Male
(mean ± sd)
Job control** 62.7±9.1 64.7±8,6 58.0±8.5
Psychological demands** 30.4±4.9 30.0±4.8 31.4±4.9
Social support** 22.7±3.2 23.0±3.3 22.1±3.1
Job dissatisfaction* 0.25±0.23 0.23±0.22 0.28±0.24
*P < 0.05; **P < 0.001 (comparisons of means by analysis of variance) / [comparações de médias por análise de variância] Range of values for Job control= 96 – 24; Psychological demands= 48 – 12; Social support= 32 - 8; Job dissatisfaction= 1 - 0
Limites de valores para controle de trabalho=96 – 24; Demandas psicológicas= 48 – 12; Suporte social= 32 - 8; Insatisfação com o trabalho= 1 - 0
that had lasted for at least one week or had occurred at least once a month over the preceding twelve months, among workers who were actively engaged in work, we can conclude that there is significant morbidity among this population.
Psychosocial work demands were posi-tively associated with MSDs in both body
areas studied. Physical work demands were associated with neck, shoulder and upper back MSDs. Moreover, among non-occupational variables, an association was found between neck, shoulder and upper back MSDs and poor physical fitness as well as between distal upper limb MSDs and females.
Table 4 - Distal upper limb MSDs and related predictors.
Tabela 4 – DMEs de extremidades superiores distais e preditores relacionados.
Independent variables Odds Ratio
(95% Confidence Interval)
Gender (female=risk) 2.25 (1.27 – 4.00)
Psychosocial demandsa (PD) 2.08 (1.20 – 2.62)
Job dissatisfactionb (JD) 1.83 (1.10 – 3.04)
b c d JD, PDR, PDMH: 0= low exposure (<median), 1=high exposure (>median) / 0= baixa exposição (<mediana), 1=alta
exposi-ção (>mediana)
a PD: 0=high social support (>median) and high job control (>median) and high psychological demand (>median) or high
so-cial support and high job control and low psychological demand (<median) or high soso-cial support and low job control (<me-dian) and low psychological demand or low social support (<me(<me-dian) and high job control and low psychological demand; 1= low social support and low job control and low psychological demand or low social support and low job control and high psychological demand or low social support and high job control and high psychological demand or high social support and low job control and high psychological demand.
a PD: 0=suporte social elevado (>mediana) e controle do trabalho elevado (>mediana) e demanda psicológica elevada
(>media-na) ou suporte social e controle do trabalho elevados e demanda psicológica baixa (<media(>media-na) ou suporte social elevado e contro-le do trabalho baixo (<mediana) e demanda psicológica baixa ou suporte social baixo (<mediana) e controcontro-le do trabalho econtro-levado e demanda psicológica baixa; 1= suporte social baixo e controle do trabalho baixo e demanda psicológica baixa ou suporte social baixo e controle do trabalho baixo e demanda psicológica elevada ou suporte social baixo e controle do trabalho elevado e de-manda psicológica elevada ou suporte social elevado e controle do trabalho baixo e dede-manda psicológica elevada.
Table 5 - Neck, shoulder and upper back MSDs and related predictors.
Tabela 5 – DMEs de pescoço, ombro e coluna alta e preditores relacionados.
Independent variable Odds Ratio
(95% Confidence Interval) Physical Demands with Manual Handling a (PDMH)
Physical Demands with Repetitivenessb (PDR) 2.96 (1.81– 4.85)
2.01 (1.25 – 3.24)
Fitness (precarious=risk) 1.94 (1.21 – 3.13)
Psychosocial demandsc (PD) 1.69 (1.02 – 2.79)
Job dissatisfactiond (JD) 1.68 (1.03 – 2.74)
a b d PDR, PDMH and JD: 0= low exposure (<median), 1=high exposure (>median) / 0= baixa exposição (<mediana), 1=alta
exposição (>mediana)
c PD: 0=high social support (>median) and high job control (>median) and high psychological demand (>median) or high
social support and high job control and low psychological demand (<median) or high social support and low job control (<median) and low psychological demand or low social support (<median) and high job control and low psychological de-mand; 1= low social support and low job control and low psychological demand or low social support and low job control and high psychological demand or low social support and high job control and high psychological demand or high social support and low job control and high psychological demand.
a PD: 0=suporte social elevado (>mediana) e controle do trabalho elevado (>mediana) e demanda psicológica elevada
(>me-diana) ou suporte social e controle do trabalho elevados e demanda psicológica baixa (<me(>me-diana) ou suporte social elevado e controle do trabalho baixo (<mediana) e demanda psicológica baixa ou suporte social baixo (<mediana) e controle do trabalho elevado e demanda psicológica baixa; 1= suporte social baixo e controle do trabalho baixo e demanda psicológica baixa ou suporte social baixo e controle do trabalho baixo e demanda psicológica elevada ou suporte social baixo e controle do trabalho elevado e demanda psicológica elevada ou suporte social elevado e controle do trabalho baixo e demanda psicológica elevada.
The findings of greater morbidity in dis-tal upper limbs of women are independent of the degree of job dissatisfaction and of psychosocial demands, for which the re-sults were adjusted. Furthermore, neither physical demands at work nor housework explained this greater morbidity among women. Biological differences mediated by hormonal factors relating to the female re-productive system have already been men-tioned as one of the possible explanations for greater morbidity among women30,31.
Another explanation could be that women report symptoms more readily. However, such results have been inconsistent, with differences in the accuracy of responses from women in these studies32. Certainly,
there are other explanations for gender differences in MSD occurrence33. Different
tasks and working styles are some of them. Psychosocial demands were found to be positively associated with MSDs. This result is compatible with reviews on this topic13,19,25. In some studies, job
dissatisfac-tion has been associated with MSDs in the lumbar region, but few positive results asso-ciating job dissatisfaction with MSD of the upper limb have been found 1,12,13. The study
reveals a higher probability of distal upper limb MSDs among workers who were more dissatisfied at work, when compared to workers who were less dissatisfied. However, considering the study design, dismissing the idea of reverse causality is not possible.
Regarding neck, shoulder and upper back MSDs, there was a greater probability of their occurrence among workers who were more exposed to physical demands related to manual handling than among those who were less exposed. These deman-ds incorporated not only load lifting but also the variables WORKING WITH ARMS ABOVE SHOULDER LEVEL and MUSCULAR EXERTION WITH ARMS AND HANDS, whi-ch have had both been cited in the literature
as associated with shoulder and neck region MSDs. The probability of neck, shoulder and upper back MSDs was also greater among workers who were more exposed to repetitive physical demands, more exposed to psychosocial demands and more dissa-tisfied with work. Gender, housework and number of years of work were not predictors for MSDs in this body area.
The odds ratio of neck, shoulder and upper back MSDs was greater among workers who perceived they had poor phy-sical fitness than among those who felt they were fitter. There is no consensus regarding the role of physical fitness in preventing MSDs 1,34. Muscle strength training and
physical exercise may prevent neck, shoul-der and upper back MSDs among workers who are exposed to tasks that require high levels of muscular exertion. The difficulties of isolating the effect of physical exercise programs carried out at the workplace are a consequence of the fact that such programs often occur simultaneously with other non-controlled changes in work organization. These scenarios may limit the assessment of the role of physical exercise programs on MSDs34.
The findings suggest that reducing neck, shoulder and upper back MSDs and reducing distal upper limb MSDs in workplaces require appropriate measures aimed at making the physical environment more suitable, with regard to equipment, machinery, tools and furniture, in order to reduce repetitiveness, the use of force and manual handling. They also suggest that or-ganizational modifications should be made in order to reduce psychological demands, extend the degree of control workers have over their work and increase social support. These programs must also consider pro-bable gender differences on occurrence of distal upper limb MSDs.
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Recebido em: 15/05/09 Versão final reapresentada em: 22/12/09 Aprovado em: 20/01/10
